From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <paulmck@linux.vnet.ibm.com>
Received: from e36.co.us.ibm.com (e36.co.us.ibm.com [32.97.110.154])
 (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
 (Client CN "e36.co.us.ibm.com", Issuer "GeoTrust SSL CA" (not verified))
 by ozlabs.org (Postfix) with ESMTPS id 46C6F2C0082
 for <linuxppc-dev@lists.ozlabs.org>; Thu, 27 Jun 2013 00:45:43 +1000 (EST)
Received: from /spool/local
 by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only!
 Violators will be prosecuted
 for <linuxppc-dev@lists.ozlabs.org> from <paulmck@linux.vnet.ibm.com>;
 Wed, 26 Jun 2013 08:45:37 -0600
Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com
 [9.17.195.106])
 by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id 0883F3E40026
 for <linuxppc-dev@lists.ozlabs.org>; Wed, 26 Jun 2013 08:45:13 -0600 (MDT)
Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245])
 by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id
 r5QEjVv7265212
 for <linuxppc-dev@lists.ozlabs.org>; Wed, 26 Jun 2013 08:45:31 -0600
Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1])
 by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id
 r5QElrbg003220
 for <linuxppc-dev@lists.ozlabs.org>; Wed, 26 Jun 2013 08:47:54 -0600
Date: Wed, 26 Jun 2013 07:45:24 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: David Laight <David.Laight@aculab.com>
Subject: Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus_atomic() to
 prevent CPU offline
Message-ID: <20130626144524.GQ3828@linux.vnet.ibm.com>
References: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com>
 <20130625202755.16593.67819.stgit@srivatsabhat.in.ibm.com>
 <20130625220026.GG3828@linux.vnet.ibm.com>
 <51CAF624.6060004@linux.vnet.ibm.com>
 <AE90C24D6B3A694183C094C60CF0A2F6026B72AA@saturn3.aculab.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B72AA@saturn3.aculab.com>
Cc: peterz@infradead.org, fweisbec@gmail.com, oleg@redhat.com,
 walken@google.com, mingo@kernel.org, linux-arch@vger.kernel.org,
 vincent.guittot@linaro.org, xiaoguangrong@linux.vnet.ibm.com,
 wangyun@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com,
 linux-pm@vger.kernel.org, rusty@rustcorp.com.au, rostedt@goodmis.org,
 namhyung@kernel.org, tglx@linutronix.de, laijs@cn.fujitsu.com,
 zhong@linux.vnet.ibm.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
 sbw@mit.edu, "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
 tj@kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org
Reply-To: paulmck@linux.vnet.ibm.com
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>

On Wed, Jun 26, 2013 at 03:29:40PM +0100, David Laight wrote:
> > Once stop_machine() is gone from the CPU offline path, we won't be able
> > to depend on disabling preemption to prevent CPUs from going offline
> > from under us.
> 
> Could you use an rcu-like sequence so that disabling pre-emption
> would be enough?
> 
> Something like rebuilding the cpu list, then forcing yourself
> to run on all the cpu.
> 
> That would be far less intrusive.

Maybe...  I must defer to Srivatsa on this question.

							Thanx, Paul